WASHINGTON -- President Barack Obama is expected Friday to announce new limits on the NSA program that collects billions of phone records from Americans, but he will call on Congress to help determine the program's future, according to current and former officials familiar with the plans.

Obama has concluded that the program has value as a counterterrorism tool, the officials said, but is also confronting difficult political realities. The sweeping nature of the National Security Agency's data warehousing has prompted serious privacy concerns, and a divided Congress is unlikely to renew it when the law underpinning the program expires next year.

Officials have said Obama's speech is part of an effort to restore confidence at home and abroad in the government's surveillance policies. While the NSA program has perhaps raised the most significant concerns about privacy advocates, other disclosures over the past eight months have generated controversy over U.S. intelligence activities.

White House officials said Wednesday that Obama's speech is still being crafted and declined to comment.

Two people familiar with the deliberations said the president is likely to emphasize that the NSA's bulk collection of phone data, which includes numbers dialed but not call content, is not something that the government should rely on except in limited circumstances related to the agency's mission.

The program was begun after the Sept. 11, 2001, terrorist attacks and was placed under court supervision in 2006. Analysts are supposed to access the data only for the purpose of seeking leads in counterterrorism investigations.

The White House has opted not to shift the job of holding the phone records for the NSA to phone companies, as a presidential advisory group recommended in a report last month. The idea provoked opposition from company executives.

Current and former officials had mixed views on the likely effect of any new limits on the program. "There's going to be substantive changes," said one U.S. official briefed on the deliberations who was not authorized to speak on the record. Other officials have said that the constraints would not be that significant.

The decision to turn to Congress for guidance, first reported in The New York Times, has drawn fire from NSA defenders and critics alike, underscoring the challenge Obama faces.

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